This invention relates to turbines, and more particularly, a speed limiting mechanisms for turbines.
Turbines have operating characteristics particular to their configuration. For example, axial turbines, which are often used as starters for gas turbines or other types of engines, have a generally linearly decreasing torque versus speed characteristic. At the maximum speed of an axial turbine, the turbine experiences a no-load condition in which there is near-zero torque. Such turbines may fail at the maximum operating speed because the turbine is highly stressed. Therefore, it is desirable to reduce the operating speed of the turbine at the no-load condition. Turbine speed limiting devices are known. For example, the rotational speed of the turbine may be monitored and reduced by modifying the powering characteristics. However, it may be desirable to utilize an additional speed limiting device or use a different speed limiting device altogether than those currently available.
Previously, devices have been used in the diffuser portion of the starter, where fluid is expelled from the turbine, to increase the efficiency of the rotor. Devices such as splitters arranged in the diffuser portion have been used to increase the efficiency and speed of the turbine by enhancing the flow characteristics through the diffuser. Devices such as these may increase the undesirable stresses within the turbine by increasing the speed. The aerodynamic characteristics of the turbine rotor may be changed to reduce the speed of the turbine at the no-load condition, for example, by changing the profile of the rotor blades. Such a change to the rotor blades may undesirably impact other operating characteristics of the turbine and therefore may not be desirable. Therefore, what is needed is a suitable speed limiting device for reducing the turbine speed at the no-load condition without modifying the aerodynamic characteristics of the turbine rotor.
The present invention provides a starter including a housing defining a fluid passageway with an inlet and an outlet. A turbine rotor is supported in the housing and includes blades arranged in the passageway between the inlet and the outlet. The rotor rotates within the passageway at a speed with a fluid exiting the blade toward the outlet. A spoiler is arranged in the passageway between the rotor and the outlet. The spoiler deflects the fluid exiting the rotor blade. The disturbance reduces efficiency and reduces rotor speed. Preferably, the present invention spoiler is utilized to reduce the maximum speed at the no-load condition. However, the spoilers may be used to reduce the speed at any load condition. The angle, number, position, and other characteristics of the spoiler may be tailored for the particular turbine and a particular speed for which it is desirable to reduce.
Accordingly, the present invention provides a suitable passive speed limiting device for reducing the turbine speed at the no-load condition without modifying the aerodynamic characteristics of the turbine rotor.